As is commonly known, an optical storage disc comprises at least one track, either in the form of a continuous spiral or in the form of multiple concentric circles, of storage space where information may be stored in the form of a data pattern. Optical discs may be read-only type, where information is recorded during manufacturing, which information can only be read by a user. The optical storage disc may also be a writeable type, where information may be stored by a user. Since the technology of optical discs in general, the way in which information can be stored in an optical disc, and the way in which optical data can be read from an optical disc, is commonly known, it is not necessary here to describe this technology in more detail.
Optical discs have found widespread use as information carrier, not only for storing computer data, but also for making audio and/or video recordings. Apparatus are available for allowing a user to make his own recordings on writeable discs. Also, audio publishing companies or video publishing companies publish pre-recorded discs, which are read-only discs (ROM); play-back apparatus are available for allowing a user to play such discs. In such play-back apparatus, indicated hereinafter simply as player, a disc drive component reads and decodes the data recorded on disc, and a video stream and/or audio stream is generated, suitable for display via a display device such as a television apparatus, a monitor, a loudspeaker, etc. This is explained in the following example.
A movie may contain several elements, indicated as follows:                Moving pictures, i.e. the actual pictures of the movie, to be displayed on the TV screen. The contents of the moving pictures are stored in a video elementary stream.        Graphics pictures. Graphics pictures are overlayed on the moving pictures like a picture-in-picture presentation. Graphics picture are used for transmitting subtitles. They may consist of background graphics (e.g. a still picture) and some text. The contents of the graphics pictures are stored in a graphics elementary stream, so a user has the option of viewing the movie with or without graphics. Usually, a user is given the option to choose a language, in which case different graphics pictures are provided, associated with different languages. In such case, the movie is accompanied with a set of multiple graphics elementary streams, one for each language.        Audio signals. The audio signal of a movie consists of background audio with spoken text, and this combination is stored in an audio elementary stream. Usually, a user is given the option to choose a language, in which case the spoken text is different for different languages while the background audio is the same for all languages. In such case, the movie is accompanied with a set of multiple audio elementary streams, one for each language.        
A combination of multiple elementary streams (for instance: moving pictures+graphics+audio) can be transmitted in one Transport stream. Each transport stream is stored as a separate file.
Traditionally, an information carrier contains only one version of the movie. With the ongoing development of optical discs, especially the increase in data storage capacity, it has become possible for the information carrier to contain two or more versions of the movie, allowing a user to select which version the wishes to see. For instance, one user may wish to see the movie in its original version, but another user may wish to have subtitles. Yet another user may prefer to hear the spoken text in his own language.
According to the state of the art, especially the well-known DVD-VIDEO standard, several different versions of the audio elementary stream and the graphics elementary stream are recorded in one transport stream, packets of the elementary streams being multiplexed in the transport stream. Depending on a user's choice, only one of the several different versions of the audio elementary stream is selected for decoding during playback, and only one of the several different versions of the graphics elementary stream is selected for presentation during playback.
So, it is for instance possible that an original English-language movie is to be published with optional French-spoken text and optional German spoken text. In that case, there is a first audio elementary stream containing the original English-spoken text, a second audio elementary stream containing the French-spoken text (translation 1), and a third audio elementary stream containing the German-spoken text (translation 2).
Also, it is for instance possible that a movie is to be published with English, French and German subtitles. In that case, there is a first graphics elementary stream containing the English text, a second graphics elementary stream containing the French text, and a third graphics elementary stream containing the German text.
The above applies already in the case of only one version of the moving pictures, i.e. video elementary stream. However, it is also possible that the information carrier contains two or more alternative versions of the moving pictures, where the same scene is viewed from different angles. This will be indicated as a multi-angle movie. Since the alternative versions of the moving pictures always relate to the same scene, the audio and graphics may be the same for all these alternative versions.
In theory, it would be possible to multiplex the plurality of alternative video elementary streams into the transport streams. During playback, the entire transport stream would be read, and only the selected video stream, audio stream and graphics stream would be decoded. However, in view of the fact that the bit rate associated with one video elementary stream is already quite high (more than 20 Mbps), this approach would result in very high bit rates, too high in relation to the read rate from the drive which is 54 Mbps for the BD-ROM drive.
According to the above-mentioned DVD-VIDEO standard, this problem is avoided by generating a plurality of individual alternative transport streams associated with the alternative video elementary streams, i.e. each of the plurality of alternative video elementary streams is combined with the same set of multiple audio elementary streams and graphics elementary streams; during playback, only the one transport stream associated with the desired viewing angle is read, and only the selected audio stream and graphics stream is decoded. Thus, the information relating to audio and graphics is recorded multiple times (as many times as the number of alternative video elementary streams). A disadvantage of this approach is that, in case the audio and graphics information is the same for all viewing angles, storage space is wasted.
In principle, it would be possible to store each alternative transport stream as one continuous recording, so that the different transport streams are physically recorded in different disc sections. This would be adequate, if a user could only make a choice at the beginning of the playback. However, in multi-angle video, a user is given the possibility to change from one viewing angle to any of the other viewing angles at any desired moment. This involves, during playback, a jump from the current reading location in the current transport stream to the corresponding reading location in the transport stream of the user's choice. The required jump distance would be large to such extent that a very large video buffer would be necessary to assure continuous display. Also, the time between the user entering his choice (e.g. pressing a button) and the system responding by changing the presentation from one viewing angle to the other viewing angle would be relatively long, to such extent that it is to be expected that the user, getting impatient, presses the button again.
In order to avoid these problems, the above-mentioned DVD-VIDEO standard provides for an interleaved recording of the different transport streams. More particularly, each transport stream is divided into relatively small transport stream pieces, indicated as angle blocks; the angle blocks of the different transport streams are interleaved in one stream. This is schematically illustrated in FIG. 1, which shows the contents of a portion of a track of a record carrier (optical disc), for an illustrative example where a movie is recorded in three different viewing angles. The record carrier contains three different information streams TS1, TS2, TS3.
Each information stream is divided into angle blocks AB1(i), AB2(i), AB3(i), index i indicating the order of display. A combination of three angle blocks AB1(i), AB2(i), AB3(i) is indicated as an interleaved unit IU(i). Each angle block ABj(i)(j=1-3) contains a multiplex of one video elementary stream VSj(i) and multiple audio and graphics elementary streams ASj,k(i) and GSj,m(i). In the example shown, k=1-2 and m=1-3. Within one interleaved unit IU(i), the three audio elementary streams ASj,k(i) of each angle block ABj(i) are mutually identical, and the three graphics elementary streams GSj,m(i) of each angle block ABj(i) are mutually identical.
Assume that a user is watching version 2 of the movie, and has selected the second audio stream AS2,2 and the third graphics stream GS2,3 associated with the second movie version. In respect of interleaved unit IU(i), a disc drive reads angle block AB2(i); at the end of this angle block, the disc drive jumps to the beginning of the next angle block AB2(i+1) of the same transport stream TS2 in the next interleaved unit IU(i+1). Thus, the entire transport stream TS2 is read from disc; the corresponding video stream VS2, the selected audio stream AS2,2 and the selected graphics stream GS2,3 are decoded and displayed.
An important disadvantage of this prior art recording method is that each audio elementary stream is recorded three times, and that each graphics elementary stream is recorded three times (in the above-mentioned example). This consumes storage space, and reduces the total playing time of the disc.
It is an important objective of the present invention to overcome or at least reduce this disadvantage.